1. Field of the Invention
The present invention relates to a battery comprising a cathode, an anode including tin-containing alloy powders, and an electrolyte.
2. Description of the Related Art
A large number of small-sized portable electronic devices such as camera/VTR (video tape recorder) combination systems, cellular phones, laptop computers or the like have come into widespread in accordance with recent advances in electronics, and a development for reducing their sizes and weights has proceeded. Accordingly, a development in compact and lightweight batteries having a high energy density, specifically secondary batteries as portable power sources used in the portable electronic devices has proceeded. As such a secondary battery, for example, a battery which uses a graphite material using intercalation reaction of lithium ions into graphite layers, or a carbon material using an application of insertion/extraction reaction of lithium ions into/from pores as an anode material have been developed and have been in practical use.
However, in accordance with a recent increase in performance of portable devices, a demand for capacity has been growing, so the battery is required to have a characteristic in which no decline in capacity occurs in spite of repeated cycles of charge and discharge, that is, an excellent charge-discharge cycle characteristic. Moreover, in accordance with diversification of use conditions of the devices, a demand for a battery exhibiting an excellent capacity at high load has been growing. As a method of obtaining such characteristics, it can be considered that light metal such as lithium metal or the like is used as is as an anode material. However, in this case, in a charging process, the light metal in dendrite form is likely to be deposited on an anode, and a current density becomes extremely high at a tip of a dendrite, so a charge-discharge cycle characteristic may decline due to the decomposition of an electrolyte or the like, or when the dendrite excessively grows to reach a cathode, an internal short circuit may be induced.
In order to inhibit the deposition of lithium in dendrite form, it is considered that a specific alloy is used as an anode active material, and during charge, lithium deposited on a surface of the anode is alloyed with a base metal of an alloy of the anode active material to be introduced into the alloy. As such an alloy, lithium-lead (Pb) alloy (for example, refer to Japanese Examined Patent Application Publication No. Hei 3-53743, Hei 5-34787, Hei 7-73044 and Hei 8-138654) or a bismuth (Bi)-tin (Sn)-lead-cadmium (Cd) alloy (for example, refer to Japanese Examined Patent Application Publication No. Hei 4-47431 and Hei 3-64987) have been disclosed, however, lead, bismuth and cadmium are not preferable in the viewpoint of recent environmental protection.
Moreover, although a method using a silicon (Si) alloy which causes very little damage to the environment has been proposed (refer to Japanese Unexamined Patent Application Publication No. Hei 7-302588, Hei 10-199524, Hei 7-326342, Hei 10-255768 and Hei 10-302770), the reaction between the silicon alloy and an organic solvent is so large that the charge-discharge cycle characteristic is poor, so it could not be put to practical use.
Further, a method using tin or a tin-containing alloy has been proposed. As the tin-containing alloy, for example, alloy materials of tin and nickel (Ni) (refer to Japanese Examined Patent Application Publication No. Hei 4-12586, Japanese Unexamined Patent Application Publication No. Hei 10-162823 and Sho 10-308207), alloy materials of lithium, aluminum (Al) and tin (refer to Japanese Unexamined Patent Application Publication No. Sho 61-66369), alloy materials of tin and zinc (Zn) (refer to Japanese Unexamined Patent Application Publication No. Sho 62-145650), materials of a tin alloy containing 1 wt % to 55 wt % of phosphorus (P) (refer to Japanese Unexamined Patent Application Publication No. Hei 8-273602), Cu2NiSn and Mg2Sn (refer to Japanese Unexamined Patent Application Publication No. Hei 10-223221), alloy materials of tin and copper (Cu) (refer to Japanese Unexamined Patent Application Publication No. Sho 10-308207), materials of a mixture of a tin-containing phase which absorbs lithium, and a phase made of manganese (Mn), iron (Fe), cobalt (Co), nickel and copper which does not absorb lithium (refer to Japanese Unexamined Patent Application Publication No. Hei 11-86854) have been disclosed.
However, in the case of a battery using tin or a tin-containing alloy, a problem that the battery cannot fully satisfy requirements for the capacity, the charge-discharge cycle characteristic and a load characteristic arises. As a cause of the problem, it is considered that when the materials absorb lithium, the materials expand. For example, it is known that in an alloy containing pure tin and lithium at a ratio of 1:4.4, the pure tin expands approximately 3.6 times, and when the tin-containing alloy absorbs lithium, it expands (refer to Electrochimica Acta 45(1999)31). In the case of using a conventional graphite material, expansion of the anode occurs, however, compared to an expansion coefficient of the material, an expansion coefficient in the case of using tin is much larger. Compared to tin, an expansion coefficient of the tin-containing alloy can be greatly improved (refer to Journal of the Electrochemical Society 148(5)A471(2001)), but it cannot satisfy requirements for practical use.
Further, according to Japanese Unexamined Patent Application Publication No. Hei 6-187971, in order to improve the charge-discharge cycle characteristic, a secondary battery using an anode made of alloy powders containing lithium with a porosity of 20% to 35% has been disclosed, although, an average voltage and a capacity of the battery is so low that the battery cannot obtain a necessary capacity for use especially in portable devices.